Method of attaching solder balls to BGA package utilizing a tool to pick and dip the solder ball in flux

ABSTRACT

A method of attaching solder balls to a BGA package using a ball pickup tool. An array of solder balls is formed on a first substrate for interconnecting with conductive sites on another substrate. The ball pickup tool picks up balls with a vacuum suction from a fluidized ball reservoir and utilizes a puff of gas to release the solder ball(s) carried thereon to conductive sites of a substrate for bonding thereto. In another embodiment, the bond pads of a substrate are coated with a flux or adhesive and lowered into a fluidized ball reservoir for direct attachment of solder balls.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/167,763,filed Oct. 7, 1998, now U.S. Pat. No. 6,595,408, issued Jul. 22, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor device manufacturing.More particularly, the instant invention pertains to methods andapparatus for handling solder balls in forming ball-grid-arrays (BGAs).

2. State of the Art

Integrated circuit semiconductor devices (ICs) are small electroniccircuits formed on the surface of a wafer of semiconductor material suchas silicon. The ICs are fabricated in plurality in wafer form and testedby a probe to determine electronic characteristics applicable to theintended use of the ICs. The wafer is then subdivided into discrete ICchips or dice, and then further tested and assembled for customer usethrough various well-known individual die IC testing and packagingtechniques, including lead frame packaging, Chip-On-Board (COB)packaging, and flip-chip packaging (FCP). Depending upon the die andwafer sizes, each wafer is divided into a few dice or as many as severalhundred or more than one thousand discrete dice.

Interconnection of discrete semiconductor packages onto a substrate suchas a printed circuit board (PCB) is often accomplished with solderpreforms having spherical, near-spherical or other shapes. In a processusing a ball-grid-array (BGA), spherical or near-spherical solder ballsare attached to prefluxed metalized locations on a workpiece such as acircuit board or a semiconductor device. The workpiece is then heated,typically at temperatures of 183° C. or greater, to reflow the solderballs, and the solder balls become attached to the metalized locationsduring subsequent cooling. A semiconductor package or circuit boardhaving a corresponding but reversed pattern of connection sites may thenbe aligned with the BGA and bonded to it by controlled heating in areflow furnace.

The use of flip-chip technology with solder bumps has numerousadvantages for interconnection. Flip-chip technology provides improvedelectrical performance for high frequency applications such asmainframes and computer workstations. Flip-chip interconnections are ofvery small size. In addition, easier thermal management and reducedsusceptibility to interference caused by a variety of sources areinherent.

Surface mount technology (SMT) using solder “bump” interconnectseliminates the outer package leads level of interconnection,significantly reducing the cost.

Solder bumps may be formed on a workpiece by processes of evaporation,electroplating, stencil printing and serial methods. Each of theseprocesses has particular limitations. Illustrated in U.S. Pat. No.5,672,542 of Schwiebert et al. is an example of a modified stencilprinting process.

In U.S. Pat. No. 3,716,907 of Anderson, the use of germanium hemispheresas conductive contacts is disclosed.

Relative to other types of interconnections, the use of solder preforms,in particular spherical or near-spherical balls, has proven to havesignificant advantages. One advantage is that while the solder balls areformed with significant ball-to-ball size differences, they may beeasily classified by size prior to application to a workpiece. Thus, auniform size of solder balls may be used within a ball-grid-array.

Various methods have been used for aligning, placing, retaining andfixing solder balls on an array of sites on a workpiece.

In U.S. Pat. No. 5,620,927 of Lee, a template with an array ofthrough-holes is placed on the workpiece and solder balls are introducedinto the holes by rolling the solder balls across the workpiece surface.The apparatus may be installed on a tilt table to encourage filling ofall holes. In U.S. Pat. No. 4,871,110 of Fukasawa et al., a templatehaving an array of holes is placed on a ball holder with a like array ofsmaller holes to which vacuum is applied and over which solder balls arerolled. After the array is filled with solder balls, the template andball holder with balls are removed and the exposed ends of the balls areattached to a substrate by e.g. reflow. The template and ball holder arethen pulled from the substrate, leaving a ball-grid-array ready forattachment to another substrate or workpiece.

As shown in U.S. Pat. No. 3,719,981, an array of solder balls isarranged on the tacky surface of a pressure sensitive (PS) tape foralignment through a template to solder bumps on a wafer. After thermalreflow, the template and tape are removed.

The use of a template for forming solder bumps or “balls” on a workpiecefrom flux and solder pieces is disclosed in U.S. Pat. No. 5,492,266 ofHoebener et al.

In U.S. Pat. No. 5,431,332 of Kirby et al., a template is placed overthe bond pads of a substrate, solder balls are poured over the template,and an air knife “sweeps” the surface free of excess solder balls.

The use of a ball pickup tool with an array of vacuum suction ballretainers to pull up balls from an underlying reservoir is disclosed inU.S. Pat. No. 5,088,639 of Gondotra et al., U.S. Pat. No. 5,284,287 ofWilson et al., U.S. Pat. No. 5,445,313 of Boyd et al., U.S. Pat. No.5,467,913 of Nemekawa et al., U.S. Pat. No. 5,615,823 of Noda et al.,U.S. Pat. No. 5,680,984 of Sakemi, U.S. Pat. No. 5,685,477 of Mallik etal., U.S. Pat. No. 5,687,901 of Hoshiba et al., and U.S. Pat. No.5,695,667 of Eguchi et al. In each of these publications, release of thearray of solder balls onto contacts of a substrate is accomplished byshutting off the vacuum.

U.S. Pat. No. 5,506,385 of Murakami et al. discloses the use of a singlemanipulatable suction head for picking up a solder ball, moving it to aposition above a fluxed contact pad on a substrate, and depositing it onthe contact pad.

U.S. Pat. No. 5,695,667 shows a single ball suction head which is usedto place a solder ball on a contact pad which is missing a solder ballof a ball-grid-array.

The application of flux to solder balls held in a vacuum apparatus bydipping the balls into a flux reservoir is taught in U.S. Pat. No.5,088,639 of Gondotra et al. and in U.S. Pat. No. 5,284,287 of Wilson etal.

The use of ultrasonic vibration to cause solder ball movement in theball reservoir, and to remove excess solder balls from a vacuum pickuptool, is taught in U.S. Pat. No. 5,687,901 of Hoshiba et al.

BRIEF SUMMARY OF THE INVENTION

At present, the invention is directed to methods and apparatus forhandling solder balls in forming ball-grid-arrays (BGAs) formanufacturing reliable interconnections between a semiconductor deviceand a substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following drawings illustrate various embodiments of the invention,wherein:

FIG. 1 is a perspective schematic view of an exemplary apparatusillustrating the steps of forming a ball-grid-array interconnection inaccordance with a method of the invention;

FIG. 2 is a sectional side view of a ball pickup tool useful in a methodof forming a ball-grid-array interconnection in accordance with theinvention;

FIG. 3 is a sectional side view of a ball pickup tool picking up solderballs for the formation of a ball-grid-array interconnection inaccordance with a method of the invention;

FIG. 4 is a sectional side view of a ball pickup tool in the process ofdipping into a reservoir of attachment agent to apply attachment agentto the picked up balls, in accordance with a method of the invention;

FIG. 5 is a sectional side view of a ball pickup tool following dippinginto a reservoir of attachment agent, in accordance with a method of theinvention;

FIG. 6 is a sectional side view of a ball pickup tool aligned with asubstrate in accordance with a method of the invention;

FIG. 7 is a sectional side view of a ball pickup tool placing solderballs onto the bond pads of a substrate in accordance with a method ofthe invention;

FIG. 8 is a sectional side view of a substrate having a ball-grid-arrayformed thereon in accordance with a method of the invention;

FIG. 9 is a generalized graphical representation of the pressure exertedon the ball seats of a ball pickup tool as a time function in a methodof the invention;

FIG. 10 is a perspective view of another embodiment of a ball pickuptool of the invention;

FIG. 11 is a sectional side view of a substrate in a process of having aball-grid-array formed thereon in a method of another embodiment of theinvention;

FIG. 11A is a sectional side view of a substrate in a process of havinga ball-grid-array formed thereon in a method of another embodiment ofthe invention wherein the substrate holder includes a screen thereon;

FIG. 12 is an enlarged view of a step in a process of forming aball-grid-array on a substrate in accordance with another embodiment ofthe invention;

FIG. 13 is an enlarged view of a step in a process of forming aball-grid-array on a substrate in accordance with another embodiment ofthe invention; and

FIG. 14 is an enlarged view of a substrate having a ball-grid-arrayformed thereon in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention comprises an improved method and apparatus for forming aball-grid-array of spherical or semi-spherical preformed solder balls onconductive sites on a surface of an electronic apparatus. The term“substrate” is used in a broad generic sense herein to include anysemiconductor device including a bare die, as well as traditionalsubstrates including circuitized boards such as printed circuit boards(PCBs). The method of the invention may be applied to the attachment ofsolder balls to any conductive site.

As depicted in drawing FIG. 1, a solder ball mounting apparatus 10includes a ball pickup tool 20, also called herein a ball pickup head.The ball pickup head 20 is connected via connector 52 to a positioner 12which controls the movement of the ball pickup head in three axes. Theball pickup head 20 is controllable along X-axis 14, Y-axis 16 andZ-axis 18 for alignment with a ball reservoir 30, an attachment agentreservoir 40, and a first substrate 50. The ball pickup head 20 may alsobe controllable about one or more axes of rotation 22, 24, 26.

The ball pickup head 20 may be as illustrated in drawing FIG. 2,comprising a body 28 with internal chamber 32. A lower plate 34 is shownwith a plurality of generally hemispherical ball seats 36, each seatconfigured to attract and retain a single preformed solder ball 60. Apassageway 38 between each seat 36 and the internal chamber 32 permitsvacuum suction 42 or gas pressure to be controllably applied to theseats 36 for alternatively retaining solder balls 60 thereon ordischarging solder balls therefrom. The internal pressure within theinternal chamber 32 is controlled by alternate activation of vacuumvalve 46 and compressed gas valve 48. The pickup head 20 may be providedwith a heater 92 by which it can quickly attain a temperature at which aparticular solder will reflow, typically 183° C. or greater, or heatedto a sufficient level to at least provide a temporary bond between asolder ball 60 and a bond pad 72, forming a ball-grid-array 62.

The pattern of ball seats 36, when inverted, is configured to match abond pad array 72 on a substrate 50 to which the balls 60 are to beattached.

As shown in FIG. 3, a solder ball reservoir 30 is configured to hold alarge number of preformed solder balls 60 and has gas sparge holes 54for fluidizing the balls within the reservoir, whereby the balls areattracted to and held by vacuum suction in the ball seats 36. Otheralternative (or additional) means for fluidizing the balls 60 may beused, such as a vibrator 63.

As depicted in drawing FIGS. 1 and 4, the solder ball mounting apparatus10 includes an attachment agent reservoir 40 containing an attachmentagent 70. The attachment agent 70 may be a flux of conventional or othercomposition and, in an embodiment of the invention, comprises a pressuresensitive adhesive (PSA) which melts when heated.

The invention encompasses the use of the formed ball-grid-array 62 on afirst substrate 50 for attachment of a second substrate 80 thereto.While the first substrate 50 is depicted as a circuit board, the secondsubstrate 80 is shown as a semiconductor device. The first substrate 50and/or second substrate 80 are moved and positioned by a positioner, notshown. The first substrate 50 has the solder balls 60 of theball-grid-array 62 attached to the bond pads 72 on the substrate 50 bythe reflow heating of the substrate 50 in a furnace. The first andsecond substrates 50, 80 are then adjoined and heated to a reflowtemperature wherein the solder balls 60 flow to adhere to the bond pads72 on the first substrate and bond pads 82 on the second substrate. Theheating may take place in a reflow furnace 90, for example, andsubstrate cooling results in a high quality electrical interconnectionbetween the two substrates.

Using this apparatus 10, several different methods may be used forattaching performed solder balls 60 to a substrate 50. In a firstmethod, illustrated in drawing FIGS. 3-9, a ball pickup head 20 islowered by movement 64 into the bed of fluidized solder balls 60 inreservoir 30. (See drawing FIG. 3.) The vacuum valve 46 is then openedto provide suction to the ball seats 36, which quickly become filledwith solder balls 60. The pickup head 20 is then retracted from the ballreservoir 30 and positioned over an attachment agent reservoir 40 bymovement 66. As shown in drawing FIG. 4, the pickup head 20 with asolder ball 60 held in each ball seat 36 is then lowered by movement 68into the attachment agent reservoir 40 so that each solder ball 60 isslightly submerged in the surface 84 of attachment agent 70. Asub-atmospheric pressure is maintained on each solder ball 60 to hold itin its seat 36.

The attachment agent 70 is any material which permits or enhancesattachment of a solder ball 60 to a bond pad 72, and temporarily holds asolder ball on the bond pad until it may be bonded by reflow thereto.Fluxes of various types are commonly used as attachment agents 70. Asparticularly taught in this application, a pressure sensitive adhesive(PSA) may also be used as the attachment agent 70. Pressure sensitiveadhesives such as those formed of epoxy, or other suitable knownadhesives, may be used.

The ball pickup head 20 is retracted from the attachment agent reservoir40 and positioned over a bond pad array 72 of a first substrate 50 bymovement 74. As depicted in drawing FIG. 5, each solder ball 60 held ina ball seat 36 of the pickup head 20 is shown with a small quantity ofattachment agent 70 on its lower surface.

In an alternative embodiment of the method, the attachment agent 70 isdirectly applied to the bond pads 72 rather than applied to the balls 60by dipping or wiping. The step of applying attachment agent 70 to thesolder balls 60 as shown in drawing FIGS. 4 and 5 is then deleted.

As depicted in drawing FIGS. 6 and 7, the ball pickup head 20 with heldsolder balls 60 is lowered by movement 76 until the balls 60 are justabove the bond pads 72, or the attachment agent 70 just touches the bondpads. Preferably, at this time, the pickup head 20 is moved slightly ina lateral direction 88 whereby each ball wipes the attachment agent 70over the bond pad surface to enhance subsequent bonding. The optimumvertical position is dependent on several factors including ball size,bond pad size, type and quantity of attachment agent 70, etc. and may befound by a process of trial and error.

As shown in drawing FIG. 7, the vacuum valve 46 is shut off and thecompressed gas valve 48 is opened for a brief time, and the “puff” ofpressure ejects the balls 60 onto the bond pads 72. The small quantityof attachment agent 70 holds each ball 60 in a generally central portionof its bond pad 72. Each ball 60 moves a very small distance, but themovement is sufficient to permit gas flow 86 from chamber 32 to escapepast the ball. Alternatively, the pickup head may be vibrated a verysmall amplitude to achieve the same result.

At this point, the method of the invention may take one of severalalternative steps.

First, the heater 92 may be used to provide a full reflow temperature tofully bond the solder balls 60 to the bond pads 72.

Second, the ball pickup head 20 may be lifted by movement 78 away fromthe first substrate 50, and the balls 60 bonded to the bond pads 72 byanother source of heat. As depicted in drawing FIG. 8, the result is afirst substrate 50 having a uniform ball-grid-array 94, ready forbonding to a second substrate 80.

Third, the ball pickup head 20 may be lifted by movement 78 from thefirst substrate 50 and the balls 60 bonded to the bond pads 72 byanother source of heat. Subsequently, a second substrate 80 is attachedto the first substrate, followed by treating at a reflow temperature,e.g., by insertion in a reflow furnace 90 or heating the substrate(s)using a block heater(s) (not shown). The result is an electronicapparatus comprising two substrates 50, 80 with a reliable BGAinterconnection therebetween.

Illustrated in drawing FIG. 9 is the time-pressure pattern of the ballpickup head 20 in the BGA formation process. Arrow 102 indicates thepoint at which all ball seats 36 are filled from the ball reservoir 30.Arrow 104 indicates the onset of dipping the balls 60 into theattachment agent 70, and arrow 106 indicates withdrawal of the ballsfrom the attachment agent reservoir 40. Arrow 108 indicates the point atwhich the vacuum 42 is shut off, and gas (e.g., air) pressure started,to eject the balls 60 from the ball seats 36. Arrow 110 indicates theend of the gas puff when the gas 44 is shut off. The gas puff is shortin duration, generally shorter than 3 seconds, and it may be less than0.5 seconds.

As shown in drawing FIG. 10, the ball pickup head or tool 20 may beconfigured to manipulate a single solder ball 60. While many variationsin the construction are possible, the pickup head 20 is generallydepicted as having a body 28 from which a hollow vacuum/pressure tip 96extends outwardly and downwardly for holding and moving a solder ball 60in a ball seat 36 at its distal end 98. The vacuum/pressure tip 96 isconnected through a valve 46 to a vacuum source 42 for attracting andholding a solder ball 60. Valves 46 and 48 may be solenoid actuatedvalves. The tip 96 is also connected through a valve 48 to a compressedgas (such as air) source 44. The airflow may be controlled to provide abrief puff of pressure to the seated ball 60 to eject it from the ballseat 36 onto the surface of a bond pad, as previously described. Thevacuum/pressure tip 96 may be lowered into a ball reservoir 30 and/or anattachment agent reservoir 40, as previously shown in drawing FIGS. 1-4.

In one embodiment of the single ball pickup head 20, a ball feeder 112comprises a solder ball vessel 114 and a tubular ramp 116 leading fromthe vessel 114 to a position adjacent the ball seat 36 when thevacuum/pressure tip 96 is retracted upwardly. A valve 118 releases oneball 60 at a time, and may comprise a pin valve operated by a solenoid.Other types of valves 118 known in the art may be used.

A gas flow from a gas source 120 may be introduced into the ball vessel114 near the ramp 116 to ensure uninterrupted ball flow in the ramp 116.

The ball feeder 112 is preferably maintained at a constant elevation, sothat the ball pickup head 20 is retracted upwardly from a lower level topick up a new ball 60.

The ball pickup head 20, whether of a single ball configuration or amultiple ball configuration, is connected to a positioner (not shown) bywhich it may be manipulated along three axes X, Y, and Z. Preferably, itmay also be rotated about at least one axis. It may be incorporated in ahigh-speed automated machine using pattern recognition and otheralignment methods, with robotic movement, and include all steps throughsolder reflow in an integral furnace.

Turning now to drawing FIGS. 11-14, an embodiment for forming aball-grid-array interconnection of preformed solder balls 60 on asubstrate 50 is illustrated. In drawing FIG. 11, a substrate 50 isretained in a substrate holder 122. In drawing FIG. 11A, the substrateholder 122 includes a screen 123 thereon, the screen 123 having aplurality of apertures therein corresponding to the array of bond pads72 on the substrate 50 to assist in the location of the solder balls 60on the bond pads 72 of a substrate 50. In any event, the substrate 50has conductive bond sites, e.g., pads 72, on a lower surface 124, andeach pad is coated or otherwise covered (at least partially) by anattachment agent 70, as shown in drawing FIG. 12. The agent 70 maycomprise flux or a pressure sensitive adhesive (PSA). The method ofapplication of attachment agent 70 to the bond pads 72 is important tothe invention only to the extent that fluidized or non-fluidized solderballs 60 from a ball reservoir 30 will adhere to the agent. Thus, theattachment agent 70 may be applied by screening, dipping, direct flow orcontact, etc.

As depicted, the method comprises lowering the array of bond pads 72into a solder ball reservoir 30 in which balls 60 are fluidized by gas56 introduced through valve 58 and passing through sparge holes 54.Alternatively or in addition to the gas sparging, a vibrator 63 may beused as shown in drawing FIG. 3. A solder ball 60 becomes directlyattached to each bond pad 72 (See drawing FIG. 13). The substrate 50 maythen be inverted as shown in drawing FIG. 14 and heated to bond theballs 60 to the bond pads 72. The substrate 50 is then ready for bondingto another substrate.

This method is very simple when compared to prior art methods of formingball-grid-arrays. No alignment of the substrate is required for ballattachment. Alternately, if desired, a screen may be used on thesubstrate holder 122 to locate the solder balls on the bond pads on thesubstrate. No solder balls are wasted. The result is a BGAinterconnection formed at very low cost.

Some variation in alignment of balls 60 on the bond pads 72 may occur,but will not affect the performance. As shown in drawing FIG. 13, theoffset 130 between the bond pad centerline 132 and the ball centerline134 is generally so small as to not be a problem. In a preferredembodiment, the bond pad side dimension 126 is minimized relative to theball diameter 128. Preferably, the side dimension 126 does not exceedthe ball diameter 128. More preferably, the side dimension 126 is notmore than one-half of the ball diameter 128, i.e., does not exceed theoverall ball radius. Thus, the attachment of more than one ball 60 to abond pad 72 is generally precluded.

In addition, the bond pads 82 of a second substrate 80 to be attached tothe first substrate 50 are made larger than bond pads 72. Thus, noproblem is encountered in achieving a reliable BGA interconnectionbetween the two substrates 50, 80.

The methods described herein present many advantages to the BGAformation process including higher reliability, lower cost, reduced ballwastage, etc.

This invention may be embodied in several forms without departing fromthe spirit of essential characteristics of the invention. Theembodiments as described herein are therefore intended to be onlyillustrative and not restrictive, and the scope of the invention isdefined by the appended claims rather than the preceding description,and all variations that fall within the metes and bounds of the subjectmatter claimed, or are equivalent thereto, are therefore intended to beembraced by the following claims.

1. A method for forming a ball-grid-array on a first substrate having atleast one bond pad using a tool comprising: providing a ball pickup toolhaving at least one orifice for picking up a preformed solder ball, saidat least one orifice in said ball pickup tool including a ball seatcontrollably connected to a vacuum source and a pressure source;providing a solder ball reservoir containing a plurality of preformedminiature solder balls; lowering said ball pickup tool into said solderball reservoir; providing a reservoir containing an attachment agent;applying vacuum suction from said vacuum source to said at least oneorifice to attract and hold at least one solder ball of said pluralityof preformed miniature solder balls within said at least one orifice;removing said ball pickup tool and said at least one solder ball fromsaid solder ball reservoir while retaining said vacuum suction; shuttingoff said vacuum suction; and applying a puff of gas pressure from saidpressure source to said at least one orifice to remove said at least onesolder ball from said at least one orifice.
 2. The method of claim 1,further comprising: aligning said at least one solder ball with said atleast one bond pad of said first substrate; and releasing said at leastone solder ball onto said at least one bond pad of said first substrate.3. The method of claim 2, further comprising: moving said plurality ofpreformed miniature solder balls upwardly within said solder ballreservoir; lowering said ball pickup tool into said solder ballreservoir and applying said vacuum suction to said at least one orificeto attract and hold said at least one solder ball within said at leastone orifice; lowering said ball pickup tool and said at least one solderball into said attachment agent reservoir whereby said attachment agentis applied to an exposed portion of said at least one solder ball; andretracting said ball pickup tool and said at least one solder ball fromsaid attachment agent reservoir.
 4. The method of claim 3, wherein saidmoving said plurality of preformed miniature solder balls upwardly insaid solder ball reservoir comprises injection of a gas stream into saidsolder ball reservoir to lift said solder balls.
 5. The method of claim2, further comprising: heating said first substrate to a reflowtemperature; and cooling a portion of said first substrate to fix saidat least one solder ball to said at least one bond pad.
 6. The method ofclaim 2, further comprising: aligning said at least one solder ball withat least one bond pad of a second substrate; and heating to a reflowtemperature said at least one solder ball for joining said firstsubstrate and said second substrate.
 7. The method of claim 2, furthercomprising: heating said ball pickup tool while aligned with said atleast one bond pad to temporarily attach said at least one solder ballto said first substrate; separating said ball pickup tool from said atleast one solder ball; aligning and contacting said at least one bondpad of said first substrate to at least one bond pad of a secondsubstrate; and heating said at least one solder ball to a reflowtemperature to join said first substrate to said second substrate. 8.The method of claim 2, wherein the step of aligning said at least onesolder ball with said at least one bond pad of said first substrateincludes: lowering said at least one solder ball to contact said atleast one bond pad; moving said at least one solder ball laterally toscrub said at least one bond pad; and centering said at least one solderball on said at least one bond pad before applying said puff of gaspressure.
 9. The method of claim 2, wherein said first substratecomprises one of a circuit board or a semiconductor device.
 10. Themethod of claim 1, wherein said puff of gas pressure results in apressure at said ball seat of about 0.001-10 psig.
 11. The method ofclaim 1, wherein a duration of said puff of gas pressure is less than0.5 seconds.
 12. The method of claim 1, wherein the step of providingsaid ball pickup tool comprises providing a pickup tool having aplurality of orifices and a screen for picking up a plurality of solderballs comprising a ball-grid-array.
 13. A method for forming aball-grid-array of preformed solder balls on a substrate for anelectronic apparatus, comprising: providing a ball pickup tool having atleast one orifice for picking up a preformed solder ball, said at leastone orifice in said ball pickup tool including a ball seat controllablyconnected to a vacuum source and a pressure source; providing a solderball reservoir containing a plurality of preformed miniature solderballs; lifting said plurality of preformed miniature solder balls insaid solder ball reservoir; lowering said ball pickup tool into saidsolder ball reservoir; providing a reservoir containing an attachmentagent; applying vacuum suction from said vacuum source to said at leastone orifice to attract and hold at least one solder ball within said atleast one orifice; removing said ball pickup tool and said at least onesolder ball from said solder ball reservoir while retaining said vacuumsuction; providing a first substrate for an electronic apparatus havingat least one bond pad; aligning said at least one solder ball with saidat least one bond pad of said first substrate for an electronicapparatus; shutting off said vacuum suction; applying a puff of gaspressure from said pressure source to said at least one orifice toremove said at least one solder ball from said at least one orifice; andreleasing said at least one solder ball onto said at least one bond padof said first substrate for an electronic apparatus.
 14. The method ofclaim 13, further comprising: moving said plurality of preformedminiature solder balls upwardly within said solder ball reservoir;lowering said ball pickup tool and said at least one solder ball intosaid attachment agent reservoir whereby said attachment agent is appliedto an exposed portion of said at least one solder ball; and retractingsaid ball pickup tool and said at least one solder ball from saidattachment agent reservoir.
 15. The method of claim 13, furthercomprising: heating said first substrate to a reflow temperature; andcooling a portion of said first substrate to fix said at least onesolder ball to said at least one bond pad.
 16. The method of claim 13,further comprising: aligning said at least one solder ball with at leastone bond pad of a second substrate for an electronic apparatus; andheating to a reflow temperature said at least one solder ball forjoining said first substrate for an electronic apparatus and said secondsubstrate for an electronic apparatus.
 17. The method of claim 13,further comprising: heating said ball pickup tool while aligned withsaid at least one bond pad to temporarily attach said at least onesolder ball to said first substrate; separating said ball pickup toolfrom said at least one solder ball; aligning and contacting said atleast one bond pad of said first substrate to at least one bond pad of asecond substrate; and heating said at least one solder ball to a reflowtemperature to join said first substrate to said second substrate. 18.The method of claim 17, wherein the step of aligning said at least onesolder ball with said at least one bond pad of said first substrateincludes: lowering said at least one solder ball to contact said atleast one bond pad; moving said at least one solder ball laterally toscrub said at least one bond pad; and centering said at least one solderball on said at least one bond pad before applying said puff of gaspressure.
 19. The method of claim 13, wherein said lifting saidplurality of preformed miniature solder balls in said solder ballreservoir comprises injection of a gas stream into said solder ballreservoir to lift said plurality of preformed miniature solder balls.